1. Field of the Invention
The present invention relates to an image processing apparatus for processing an image.
2. Related Background Art
A conventional image reading apparatus is known. In this apparatus, a photoelectric conversion means such as a CCD (charge coupled device) is moved relative to an image formed on a document surface or a film surface to scan. A read optical image is converted to an electric signal, and the electric signal is then converted to a parallel digital (bi-level or multi-level) electric signal (image signal). The digital electric signal is transferred to external equipment such as a host computer through an interface.
However, in a conventional image reading apparatus having an interface capable of transferring an image signal to a piece of external equipment, the sub-scan position must be controlled in units of lines in order to synchronize with the external equipment when the image signal is transferred. For this reason, if the apparatus employs a conventional variable magnification means for achieving a sub-scan variable magnification by changing a scan speed in accordance with a variable magnification factor, sub-scan position control in units of lines is very difficult to achieve. Furthermore, when a scanning-system driving apparatus employs a pulse motor, a problem of self-excitation frequency or vibration may occur depending on a variable magnification factor, thus limiting the range of usable variable magnification factors.
An improved image reading apparatus has already been disclosed in commonly-assigned U.S. patent application Ser. No. 513,810, filed on July 14, 1983, U.S. Pat. No. 4,635,129, and the like. An apparatus for variably magnifying an image signal has been disclosed in commonly-assigned U.S. patent application Ser. No. 590,753, filed on Mar. 19, 1984. However, a demand has arisen for a still further improved apparatus.